This application is based on Japanese Patent Application No. HEI 10-120718 filed on Apr. 30, 1998, which is incorporated herein by reference.
This application relates to a horn loudspeaker.
For a relatively large space, such as a hall and a conference room, a loudspeaker is usually disposed on a ceiling so that sound from the loudspeaker can be radiated to propagate over a wide range. For more uniform propagation of sound over a wider range, plural, e.g. two, loudspeakers may be disposed at a location, directing the respective loudspeakers in different directions.
When a plurality of loudspeakers are disposed at one location, however, sounds from the loudspeakers interfere with each other, resulting in peaks and dips in the sound pressure level in the space where the loudspeakers are installed. Such unstable sound pressure level in the space would cause listeners to feel unpleasant or make the sounds difficult to hear.
Therefore an object of this invention is to provide a horn loudspeaker which is free of peaks and dips in sound pressure level and can provide a radiation characteristic suitable for a specific use of the loudspeaker, e.g. such a characteristic as to enable uniform propagation of sound over a wide range.
A horn loudspeaker according to a first embodiment of the present invention includes an electroacoustic transducer for transducing an electrical signal applied to an input terminal of the loudspeaker to sound. The loudspeaker also includes a hollow sound conduit having its first end coupled to the transducer, for transmitting therethrough the sound emitted by the transducer to the other or second end thereof. A horn is coupled to the second end of the sound conduit for propagating the sound supplied to it from the transducer through the sound conduit, over a desired angular range in at least one propagation plane. The sound conduit is coupled to that portion of a wall of the horn which lies in a plane paralleling the propagation plane.
The horn may be generally flat in its appearance and have at least top and bottom walls facing each other. At least one of the top and bottom walls has a portion lying in a plane paralleling the propagation plane. The sound conduit is coupled to the horn at the portion paralleling the propagation plane. Accordingly, the sound from the sound conduit enters into the horn at an angle with respect to the propagation plane.
The sound conduit can be coupled to the horn at a location deviating from the center of the horn. When the sound conduit is coupled at a location deviating from the center of the horn, a larger amount of the sound is emitted in the direction in which the coupling location deviates, resulting in a higher sound pressure level in that direction.
The sound conduit can be coupled to the horn in such a manner that the sound wave from the sound conduit enters into the horn at an angle with respect to the propagation plane in which the sound wave going out from the horn advances. In this case, the sound wave can propagate easily in the direction in which it is emitted from the sound conduit, so that the sound pressure level in this direction is higher. On the other hand, it is difficult for the sound wave to propagate in the opposite direction and, therefore, the sound pressure level in this opposite direction is lower.
Thus, the amount of sound to be emitted from the horn in a desired direction, i.e. the sound pressure level in the desired direction can be changed by adjusting the position and angle of coupling of the sound conduit with respect to the horn. This enables the control of the polar radiation pattern in the propagation plane. Thus, the polar radiation pattern suitable for a specific use of the loudspeaker can be provided as desired.
The cross-section of the sound conduit in a plane perpendicular to the direction of propagation of the sound wave in the sound conduit may be in a generally straight, elongated shape, e.g. rectangular. This shape of the cross-section equivalently provides a linear sound source for the horn. The linear sound source supplies sound to the horn at an angle with respect to the direction of propagation of the sound going out of the horn.
The sound supplied to the horn from the linear sound source propagates in the propagation plane in two opposite directions perpendicular to the direction of the elongation of the cross-section of the sound conduit. This is equivalent to the use of two sound sources. The polar radiation patterns of these two sound sources and, hence, that of the loudspeaker itself can be controlled by adjusting the position where the sound conduit is coupled and the angle at which the sound conduit is coupled with respect to the horn.
The polar radiation pattern of the loudspeaker is the combination of the polar radiation patterns of the two sound sources. However, these sound sources are virtual ones, and, actually, only one real sound source, i.e. only one transducer is used. Accordingly, although the polar radiation patterns of these virtual sound sources may overlap, no peaks and dips will be developed in the overall polar radiation pattern. Therefore the sound emitted from the loudspeaker does not make listeners unpleasant, or it never happens that the sound is hard to hear.
In this arrangement, the horn may be arranged such that the sound entering into the horn from the sound conduit may propagate from the location where the sound conduit is coupled to the horn over a generally sectorial range in the propagation plane. The direction of the elongation of the cross-section of the sound conduit at the location where the sound conduit is coupled to the horn is along the bisector of the sectorial range.
For that purpose, the shape of the horn may be sectorial or semi-circular when viewed from the direction perpendicular to the propagation plane. Let it be assumed that the forward direction of the horn is the direction from the center of the sector or semi-circle toward the midpoint of the arc of the sector or semi-circle. The sound conduit is coupled to the horn with its cross-section elongated in the forward direction.
Let it be assumed that the sound conduit is coupled to the horn in such a manner that the sound enters into the horn substantially perpendicularly to the propagation plane. Then, the sound emitted from the linear sound source or two virtual sound sources propagates mainly along the two radii connecting the opposite ends of the arc of the sector or semicircle of the horn to its center. If the loudspeaker is disposed with the propagation plane extending horizontally, the sound propagates mainly rightward and leftward. Thus, the sound pressure level of the loudspeaker is higher toward the right and left of the horn and is low along the bisector of the sectorial or semi-circular horn.
If the sound conduit is tilted slightly backward, so that the sound is emitted into the horn slightly in the forward direction, the sound can advance more easily in the forward direction. Then the sounds from the two virtual sound sources propagate mainly in the rightward and leftward directions but slightly toward the bisector. This provides the maximum sound pressure level along these directions. The sounds from the two virtual sound sources are combined in the front area of the horn, and, therefore, the sound pressure level in the front area is higher than the sound pressure level provided there when the sound conduit is coupled to the horn generally perpendicularly to the propagation plane. Thus, the resulting overall polar radiation pattern of the loudspeaker is such that a generally uniform sound pressure level is generated over a relatively wide range extending right and left about the front center portion of the loudspeaker.
If the sound conduit is further tilted backward, the sound can propagate far more easily in the forward direction. Then, the sound from the linear sound source propagates in the directions much closer to the bisector than in the above-described case. In this case, a wide polar radiation pattern is provided in which the sound pressure level is generally constant over a relatively wide angular range about the bisector.
The sound conduit may be tilted rightward or leftward, with the direction of elongation of the cross-section kept to be along the bisector. If the sound conduit is tilted rightward, it is hard for the sound going out of the horn to advance rightward, i.e. the direction in which it is tilted, but the sound can advance more easily leftward, i.e. the opposite direction. Thus, the sound pressure in the rightward direction is smaller, while the sound pressure in the leftward direction is larger. If the sound conduit is tilted leftward, the sound pressure in the leftward direction is smaller, while the sound pressure in the rightward direction is larger.
The horn may be provided with a guide for guiding the sound supplied from the transducer through the sound conduit to propagate in a desired direction. The guiding of the sound by the guide can prevent discontinuity which could occur in the propagation of the sound wave. Thus, the frequency characteristic of the propagating sound is not disturbed, and, therefore, stable sound propagation can be realized.
A plurality of electroacoustic transducers and a plurality of sound conduits associated with the transducers may be provided for the horn. In this arrangement, the second ends of the respective sound conduits are coupled to the horn at locations which are close to each other, and the sound conduits are of substantially the same length.
The use of a plurality of transducers provides higher sound pressure. Also, the use of a plurality of sound conduits enables fine control of the overall polar radiation pattern of the loudspeaker.
Sounds supplied from the respective transducers through the associated sound conduits into the horn may interfere with each other in the horn. However, a peak-and-dip is not developed in a relatively low frequency range for the following reason.
A peak-and-dip is developed when interference occurs between a plurality of sounds having the same frequency which are out of phase with each other. When the sounds are out of phase with each other by a half wavelength (xcex/2), they cancel each other, and, if they are out of phase by one wavelength (xcex), they reinforce each other, resulting in the peak-and-dip phenomenon. Thus, as the phase difference between the sounds is larger, a peak-and-dip tends to occur in a lower frequency range, while a peak-and-dip tends to occur in a higher frequency range as the phase difference is smaller. Accordingly, by making the phase difference less than half of the audio frequency wavelength xcex, e.g. from about xcex/3 to about xcex/5, the generation of peaks and dips in the audio frequency range, which may cause problems in hearing, can be avoided.
According to the present invention, in order to avoid the generation of peaks and dips in the audio frequency range, the second ends of the sound conduits at which the sounds from the transducers are supplied to the horn are positioned in the proximity of each other. The xe2x80x9cproximityxe2x80x9d used herein means a distance of from about xcex/3 to about xcex/5, where xcex is the audio frequency sound wavelength. Furthermore, the lengths of the respective sound conduits, i.e. the distances of the horn from the respective transducers through the sound conduits, are made substantially equal to each other so that the difference between the lengths of the paths along which the sounds from the respective transducers travel through the horn can be small, which results in a small phase difference between the sounds.